Field of the Invention
The present invention relates to an element substrate, a printhead, and a printing apparatus.
Description of the Related Art
There is conventionally provided a printing apparatus which includes a printhead according to an inkjet method of printing using thermal energy. The inkjet printhead includes, as printing elements, heating elements (heaters) provided in portions communicating with orifices for discharging ink droplets. Then, the heating elements are applied with a current to generate heat, and discharge ink droplets by film boiling of ink, thereby executing printing.
Along with a recent increase in speed, power supplied to heaters in an inkjet printhead substrate becomes large, and noise at the time of heater driving is a problem. As a method of relaxing the noise, for example, in Japanese Patent Laid-Open No. 7-68761, the rising and falling edges of the total heater current of a chip are moderated by slightly shifting heat driving timings between heaters by a delay circuit, and thus the high-frequency noise of a power supply is relaxed, thereby improving the reliability.
However, a recent increase in number of nozzles or number of heaters simultaneously driven increases the number of delay circuits for a heat enable signal. As a result, the total delay amount of the heat enable signal increases, thereby causing a problem that heat driving is executed outside a latch cycle. If the delayed heat enable signal exceeds the latch cycle, this means that data is switched during driving. That is, desired energy cannot be applied to the heaters, and thus no printing is executed. In addition, the heaters selected in the next cycle are unnecessarily heated.
By extending the latch cycle, printing can be normally executed. However, extension of the cycle means a decrease in print speed. The print speed is ensured by shortening the delay amount of the heat enable signal so as to include the heat enable signal in the latch cycle. However, the rising and falling edges of the heater current become sharp to generate high-frequency noise, thereby causing an erroneous operation of the substrate or radiation noise.